In the medical arts, the term “occlusion” typically refers to the blocking or restriction of a normally open passage. In some instances, an occlusion is desired such as when a catheter is pinched off or temporarily collapsed into a closed state intentionally by a practitioner during a medical procedure. In other instances, an unintended occlusion could result in a potentially dangerous situation. For example, in the field of medication delivery devices and systems including so-called “syringe pumps”, typically a pre-filled medication syringe is mechanically driven under microprocessor control to deliver a prescribed dose of medication at a controlled rate to a patient through an infusion line fluidly connected to the syringe. Syringe pumps typically include a motor that rotates a leadscrew. The leadscrew in turn activates a plunger driver which forwardly pushes a plunger within a barrel of the syringe. Pushing the plunger forward thus forces the dose of medication outwardly from the syringe, into the infusion line, and to the patient intravenously. Examples of syringe pumps are disclosed in, for example, U.S. Pat. No. 4,978,335 titled “Infusion Pump with Bar Code Input to Computer” and U.S. Pat. Applic. Pub. No. 2005/0096593 titled “Syringe Pump Rapid Occlusion Detection System”. As used throughout this disclosure, the term “syringe pump” is intended to generally pertain to any device which acts on a syringe to controllably force fluid outwardly therefrom.
In such devices, an occlusion might occur when the intended and commanded forward progression of the plunger longitudinally through the syringe barrel is blocked or otherwise impeded, as when for example the infusion line tubing is kinked or otherwise structurally blocked to some degree. If the occlusion is not noticed, the patient likely would not receive the prescribed medication leading to potentially serious consequences.
Attempts to sense or detect occlusions in medical devices such as syringe pumps have therefore been made. For example, some syringe pumps detect occlusions by use of a pressure sensor that senses a force exerted by the aforementioned syringe thumb-press on the plunger driver. When the force experienced by the pressure sensor exceeds a predetermined threshold force, a processor connected to the pressure sensor generates a signal indicating that an occlusion has possibly occurred or is possibly occurring. Since syringe pumps are typically capable of accommodating a range of syringe diameters or sizes (e.g., 10 ml through 50 ml capacities) the plunger driver and pressure sensor may likely experience varying occlusion force vectors depending upon which particular size of syringe is being used in the syringe pump, leading to varying accuracy and responsiveness overall in the pump's occlusion sensing system. Since the occlusion force (F) is a function of pressure (P) exerted on the sensor over an area (A) experiencing the pressure (i.e., P=F/A) as the area decreases the pressure increases. Typically, therefore, smaller diameter syringes yield smaller sensed forces for given pressures upon occurrences of occlusions. Thus, known occlusion detection systems and methods have not been entirely satisfactory in sensing and signaling occlusions for relatively smaller diameter syringes.
Consequently, it would be useful and advantageous to provide systems for, and methods of, occlusion detection, particularly when using syringes of relatively small diameters in syringe pumps.